The influence of ergometer pedaling direction on peak patellofemoral joint forces.

OBJECTIVE: To compare patellofemoral joint forces during forward pedaling and reverse pedaling on a bicycle ergometer.

DESIGN: Experimental within-subject design.

BACKGROUND: Clinicians addressing patellofemoral pain syndrome often strive to achieve quadriceps strength while reducing forces at the patellofemoral joint. Related to this goal, previous research has shown greater activity in the quadriceps during reverse pedaling compared to forward pedaling on a bicycle ergometer, however, patellofemoral joint forces were not examined.

METHODS: Twenty-one healthy males performed 5-min exercise bouts for forward and reverse pedaling while normal and tangential pedal forces and kinematic data were collected. Inertial properties of each segment were estimated and net joint moments were calculated using Newtonian inverse dynamics. Patellofemoral joint forces (Fpf) were quantified using the equation Fpf = 2FQ . sin beta/2, where FQ is the quadriceps force and beta is the patellar mechanism angle.

RESULTS: Reverse pedaling exhibited a 110% greater peak patellofemoral joint force and a 149% greater quadriceps force than forward pedaling. Peak effective moment arm lengths were not different between conditions.

CONCLUSIONS: Reverse pedaling is associated with a greater peak patellofemoral force than forward pedaling. The peak force was influenced by the quadriceps force and not by the moment arm length.

RELEVANCE: Insufficient data exist concerning the use of reverse pedaling as an alternative to forward pedaling for rehabilitation of knee disorders. Although quadriceps activity appears greater for reverse pedaling compared to forward pedaling, greater peak patellofemoral forces contradict clinical treatment goals for patellofemoral pain syndrome and may lead to load-elicited pain or damage to joint structures.